This invention relates in general to furnances for melting metal and more particularly to a removable roof for such a furnace, a furnace having such a roof, and the process for constructing the roof.
Aluminum and its alloys melt at a relatively low temperature and therefore lend themselves to casting and recycling. Indeed, a variety of furnaces exist for melting aluminum. In one type of furnace, the entire roof may be removed, and indeed is temporarily displaced to the side of the furnace when the furnace is charged. This of course reduces the time for charging.
The typical removable roof for a melting furnace of that variety is constructed in the shape of a dome from tapered fire bricks which are set up in the traditional manner within an encircling structure such as a steel rim. The bricks possess considerable weight and, owing to the dome-shape in which they are arranged, they exert an outwardly directed force on the steel rim, causing substantial hoop stresses to develop within the rim. At ambient temperatures the rim can withstand these stresses, but the steel looses its strength at elevated temperatures, and since roof refractory bricks are exposed to the interior of the furnace, they become quite hot. So would the rim were it not for a water jacket that is incorporated into it. This, of course, maintains the temperature of the steel rim considerably less than that of the dome-shaped array of fire bricks which it contains--indeed at a temperature low enough to preserve the strength of the steel. The water jacket renders the roof more complex and adds appreciably to the cost of constructing and maintaining it.
Aside from the foregoing, a domed roof with its multitude of bricks, all in effect keyed together, is extremely difficult to repair. More often than not all of the brickwork must be reconstructed when only a small portion of it fails.
Cast roofs, that is roofs formed from castable refractories, are normally flat and do not require rims to contain them, but this type of roof construction has heretofore been installed only on fixed roof furnaces. Indeed, to construct such a roof, a form is erected within the furnace beneath an array of anchors which are suspended from beams. The refractory is then mixed and poured onto the form around the anchors. Once the refractory has set, the form is disassembled and removed through a clean-out door in the side of the furnace.
The present invention resides in a melting furnace having a removable roof provided with a castable refractory as well as in the process for constructing the roof.